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NICOTINE SULPHATE IN A DUST 
CARRIER AGAINST TRUCK- 
CROP INSECTS 



ROY E. CAMPBELL 

Scientific Assistant, Truck-Crop Insect InvtwtiKations 




UNITED STATES DEPARTMENT OF AGRICULTURE 
DEPARTMENT CIRCULAR 154 



Contribution from the Bureau of Entomology 
L. O. HOWARD, Chief 



Washington, D. C. 



Issued February 21, 1921. 



WASHINGTON : GOVERNMENT PRINTING OFFICE : 1921 



..vA.,..^aA,s^JJ: 



I \pwARv OF CON(jHtSi: 

OCT 3 1933 



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NICOTINE SULPHATE IN A DUST CARRIER AGAINST 
TRUCK-CROP INSECTS. 



INTRODUCTION. 



The successful use of nicotine sulphate in dust form by Ralph E, 
Smith, of the University of California, in 1916 in the control of 
the walnut aphis Chroma pirn juglandicola. Kalt.), a serious pest 
in the walnut sections of southern California, induced the writer to 
test this insecticide against insects injurious to truck crops. As 
first used by Prof. Smith, the dust was made by grinding up stems 
and refuse tobacco, with the inevitable result of a variation in the 
nicotine content. To this variation was laid the cause for the 
diversity of results in different orchards where the amount of mate- 
rial used and methods of application were the same. Since there 
was no way to regulate the nicotine content in ground tobacco. Prof. 
Smith decided to use a certain amount of prepared and standardized 
nicotine sulphate in an inert dust carrier. After extended experi- 
ments it was found that kaolin possessed the necessary character- 
istics for fineness, lightness, and inertness for an ideal carrier. Fur- 
ther experiment showed that a mixture of 2 per cent by weight of 
40 per cent nicotine sulphate in kaolin gave a thoroughly satisfactory 
kill of aphids. It was also found that by using 25 per cent of finely 
pulverized unslaked lime in the carrier, the slaking and heat there- 
from took up the moisture in the nicotine-sulphate solution and 
that a chemical reaction took place, forming calcium sulphate and 
.free nicotine, which latter proved to be much more toxic to the 
aphids than the nicotine sulphate. 

PROCESS OF MANUFACTURE. 

The original process of manufacture was as follows : The material 
was first run through a sifter and mixing box such as bakers use. 
The proper amount of kaolin and lime was put in this box, wliich 
was about 5 feet long by 2 feet square, and had a capacity of 400 
pounds. At one end was a small tank into which the desired amount 
of nicotine sulphate solution was placed, a 2 per cent mixture re- 
quiring 8 pounds, a 5 per cent mixture 20 pounds, etc. So that the 
mixing would be thorough this solution was blown into the mixing 
box as a fine spray. From the mixer and sifter the dust went 
20861°— 21 3 



4 Circular lofy, U. S. Dept. of Agriculture. 

through an additional sifter, so that when the process was complete 
the materials would be entirely blended into a fine dust, such as would 
easily go through a 2()()-mesh screen. 

At present the process is similar, but on a much larger scale. 

The use of this dust was so successful and so universally satisfac- 
tory that the California Walnut Growers' Association, one of the 
large cooperative farmers' organizations of California, decided to 
manufacture it, not only for its own members but also for outsiders. 
During the 1920 season 10 tons of 40 per cent nicotine sulphate were 
used in making approximately 450 tons of the dust. During the 
season when the walnut apliis was at its height the one plant turned 
out almost 100 tons per week. As a result of the marked success of 
this method of control, spraying for the walnut aphis has been en- 
tirely superseded by dusting. 

The dust is easily carried by the wind, and hence the best results 
are obtained when little or no air is moving, and also when there is 
a slight amount of moisture on the foliage. Many dusters make a 
practice of beginning at daylight and continuing up to about 10 
o'clock. Since an acre can be covered in about one-half hour, a com- 
paratively large area may be gone over. It is often possible to con- 
tinue later in the morning, so that if an early start is made an aver- 
age of 15 to 20 acres per day can be dusted, which is in decided con- 
trast to the 3 or 4 acres which it is possible to spray in the same length 
of time. Several operators have tried dusting at night, but although 
this practice was successful, it has not been followed to any extent. 

TYPE OF MACHINE USED. 

In the commonest type of duster the hopper holds 100 pounds of 
dust. A mechanical and easily regulated device allows the desired 
amount of dust to feed into the pipe under the hopper, through which 
the air is blown from the large, rapidly revolving fan. From the 
pipe the dust passes into a hose 4 inches in diameter and about 12 
feet long. The operator moves about under the tree with this hose, 
directing the blast of dust, until the tree is covered. Power to run the 
fan is derived from a gasoline engine. The duster and engine can 
be mounted on a small wagon or sled. Such an outfit retails at about 
$375 complete, while a walnut sprayer would cost not less than $900. 
The duster requires a driver and one operator, while the sprayer 
takes two operators, and sometimes a driver. An extra sack or two 
of dust can be carried with the outfit and other sacks placed at the 
ends of the tree rows, so that refilling the hopper is a matter of only 
a few minutes' time, while with the sprayer it is necessary to stop 
work and go to the source of water to refill, which often may be 
some distance. 



Nicotine Sulphate in a Dust Carrier. 5 

ACTION OF THE DUST. 

The action of this dust on insects and mites is similar to that of 
the nicotine sulphate in liquid spray, except that it is very much more 
rapid. Within a minute or two after the application of the dust, 
aphids or other insects show extreme distress. They become agi- 
tated, elevate their abdomens as if they were trying to stand on their 
heads, and soon fall. \^lien one is standing under an infested walnut 
tree just after it has been dusted the falling of aphids reminds one 
of a gentle rain. On other plants the effect is as immediate, but not 
quite so striking. 

The after effect has been observed to be quite lasting also, especially 
on young aphids. If any young are produced by an adult which was 
not killed, or by a migrant several days after the application was 
made, they will immediately be overcome by the dust. 

USE AGAINST TRUCK-CROP INSECTS. 

When nicotine sulphate applied as a dust became so strikingly suc- 
cessful in controlling the walnut aphis, it was decided to test it 
against some of the insects, particularly aphids, affecting truck and 
associated crops. 

THE MELON APHIS. 

Tlie melon aphis {Aphis gossypii Glover) has been a serious enemy 
of the melon, squash, cucumber, and some other crops in southern 
California for a number of years, the damage varying from year to 
year, and in different localities, from slight and scattered infesta- 
tions of little consequence to severe infestations causing a total loss 
of the crop. From the fact that the insect feeds almost entirely on 
the lower surface of the leaves, causing many of the latter to curl, 
it has been difficult to obtain a satisfactory control with liquid spray. 
If sufficient time and care are taken to insure the covering of all the 
leaves, particularly the undersides, the operation is too expensive, 
and if extreme care is not taken the percentage of aphids killed is too 
low to make the spraying worth while. 

Tests of nicotine sulphate dust did not give very good results at 
first, but when a mixture containing more nicotine sulphate was used, 
the results improved accordingly. It was soon discovered that while 
the walnut aphis was easy to kill with a 2 per cent strength, for 
practically all other aphids a higher strength was required. When 
extreme care was taken and a very thorough application made, the 
weaker strength gave good results, but in commercial practice it 
was found that a 5 to 7j per cent strength of 40 per cent nicotine 
sulphate was \Qvy much better. 



6 Circular 15^, U. S. Dept. of Agriculture. 

The most satisfactory type of machine for melons was found to be 
a hand-operated bellows duster such as is shown in figure 1. With 
such a machine one man can cover not less than 2 acres of full- 
grown cassabas or muskmelons a day, using about 50 pounds of dust 
per acre, costing 12 cents a pound for 5 per cent strength and 15 cents 
for the 7 J per cent. 

It is characteristic of the melon aphis in southern California that 
it appears early in the season, when the plants are small, and seri- 
ously infests scattered portions of the field. If left unchecked the 
plants will be sufficiently damaged to produce little or no fruit, and 
often the aphids will spread to all parts of the field. Such infesta- 




FiG. 1. — Hand-opeiated bellows type of duster used in applying nicotine sulphate 
dust to melons for the melon aphis. 

tions are a nuisance to spray with an outfit of any size, while knap- 
sack, or small compressed-air sprayers, are almost equally unsatis- 
factory. With a duster of the type shown in figure 1, however, it is 
a simple matter to go over the field as often as necessary, dusting tlie 
infested plants and thus stopping the damage and checking the 
spread. 

Figure 2 shows a power-operated fan blower which was used in 
a badly infested cassaba melon field. This machine killed a large per- 
centage of the aphids, and covered almost an acre per hour, but 
was somewhat wasteful of material, using from 75 to 100 pounds 
per acre. It was apparent that this amount could be reduced with 



Nicotine Sulphate in a Dust Carrier. 7 

some mechanical changes and by using a smaller exit pipe. This 
machine would be advantageous for large acreages and where it is 
desired to get over a field in a very short time. The outfit, with 
engine, costs about $150, while the hand duster does not cost over $20. 
Dusting for the aphis was found to be equally successful on all 
kinds of melons, cassabas, cucumbers, etc. 

THE CABBAGE APHIS. 

The cabbage aphis (Aphis hrassiccw Ij.) often does serious damage 
in California. The bulk of the cabbage crop is grown in the winter. 




Pig. 2. — Power-operated fan duster used with success in a badly infested melon field. 



and usually the aphids are kept in check by rains and cold weather. 
For several years, however, the early winter rains have been lacking 
and the temperature very mild, Avhich has resulted in a serious aphis 
infestation of thousands of acres of cabbage and cauliflower. 

Here, again, because of the fact that the colonies of aphids are 
usually on the undersides of the leaves, or are protected by the com- 
pact foliage of the growing head, it is difficult to get a satisfactory 
killing by spraying. The difficulty is further accentuated by the 
fact that the aphis colonies cause the leaves to curl, making it almost 
impossible to reach them with a spraj^ When the dust was tried in a 
badly infested cabbage field, a high percentage of the aphids was 
killed. The cloud of dust hovering over and about the plant pene- 



8 Circular 15^, U. S. Dept. of Agriculture. 

trated to all parts, and in most cases e\eii re:iched the aphids in the 
curled leaves. (Fig. 3.) 

A preliminary experiment to determine the effectiveness of the 
different strengths of nicotine sulphate in the dust gave the following 
results (Table 1). A careful estimate of the aphids on a number of 
different plants Avas made both before nnd after dusting, and the 
percentage of killing taken from that. 

Tahi.k 1. — Effc(tircnG>fs of different strenytlis of nirofiiir sulithaie in dunt 
against the cahhafir niiUin. 

Strength of 40 per cent nicotine sulphate, by 

weight per cent__ 2 4 6 8 10 ' 10 

Percentage of apliii Is killed <S2. S 92.4 96.7 97 9S. .S 91.8 



^' 






'^^i^-Mm&mm^ "^ '^ 









-• • - ■ ■ ■ n, 







I'll.. :;. — Duf-tinj; liir tlir t',ililia.i,'c npliis. Note cloud ol' diisl lidsi'iiiii; about aud coiu- 
plotely fovoiing all parts of infested plants. 

P\irther experiments confirmed the above, indicating that the per- 
centage of killing rose considerably from 2 to 6 per cent strength, 
but above that the rise was small and did not justify the additional 
expense of the extra nicotine sulphate. It was also determined that 
for ordinary commercial purposes the 5 per cent strength was the 
most satisfactory, considering both the killing obtained and the cost 
per pound. 

A badly infested cabbage field in Orange County was dusted by 
hand machines such as that shown in figure 3. Mexican laborers were 
employed, one man covering an average of 2 acres a day, using 30 

'This dust was atxiut '.i monllis old. and. lla^■ini; Iweii ki'pl in a ic\inn.v sack. Intd lost 
some of its .stienfrtli. 



Nicotine Sulphate in a Dust Carrier. 9 

pounds of dust per acre, on cabbage less than half grown, while on 
cabbage more than half grown one man averaged If acres a day, 
using 50 pounds of dust per acre. (See Table 2.) The cost of the 
dusting with 7^ per cent strength of dust was as follows : 

Table 2. — Cost of (histing cabbage for the cabbage aphis. 

On cabbage less than half grown: 

Dust, 30 pounds, at 15 cents $4. 50 

Mexican labor, * day at $3.25 1.65 

Total cost per acre 6. 15 

On cabbage over half grown : 

Dust, 50 pounds at 15 cents 7.50 

Labor, IJ acres per day ! 1. 85 

Total cost per acre 9. 35 

About the same time a field of badly infested cabbage was sprayed 
with 40 per cent nicotine sulphate and soap by a commercial sprayer. 
The work was done with a power outfit, two men following behind 
with short spray rods attached to 25-foot lines of hose. With this 
outfit it was possible to cover only 3 or 4 acres per day, at an average 
cost of $12 per acre, including rent of machine and team. The per- 
centage of aphids killed was low, averaging not over 70 per cent for 
the entire field. On the other hand, an average killing of 90 per cent 
or over is easily obtained with the dust when carefully applied. 

THE ONION THRTPS. 

Extensive plantings of onions in the Coachella Valley have often 
been severely damaged by the onion thrips {Thrips tahaci Lind.). 

Control by spraying with a nicotine sulphate and soap solution 
has been successful from a standpoint of killing efficiency, but the 
practice was unsatisfactory for the following reason : 

Bulb onions are planted in rows 12 to 14 inches apart, and irri- 
gating flumes cross the fields about every 660 feet, with the onion 
rows reaching up to the flumes. On account of the closeness of the 
rows and the irrigating flumes across the fields, the operation of 
horse-drawn spray machines causes considerable damage to the 
onions. As it is impossible to drive across the flumes, the frequent 
turning around damages many onions. Practically all cultural work 
is done with burros or ponies, having small feet, but a spray machine 
of any size would require large horses, which would cause further 
damage to the bulbs. 

A trial of the nicotine sulphate dust on the onion thrips killed from 
87 to 97 per cent. A trial on a commercial scale, using the hand- 



10 Circular ITA, U. S. Dept. of Agriculture. 

operated bellows duster (fig. 4) showed that one man could cover 
from 2i to 3 acres a day, using from 40 to 50 pounds per acre, which 
made a total cost, including labor at $3.50 per da^J^, of from $6 to $7 
per acre. . 

A field of seed onions near by, of similar size but planted in 24-inch 
rows, was sprayed with a traction sprayer, which had a stationary 
boom covering five rows at a time. With this outfit it was possible 
to cover up to 6 acres a day, although this depended on the dis- 
tance it was necessary to go for water to refill the tank. An average 
of 150 gallons of spray per acre was used (with a weight of 1,200 
pounds) . The total average cost per acre, including hire of team and 




Fig. 4 — Du«tiug ouious with banU-yperated bellows duster. 

two men, was $4.40, and this amount would be approximately doubled 
for the bulb onions, grown in the 12 to 14 inch rows. 

A small power-operated duster that could be used in an infested 
onion field has an arrangement of pipes from the blower so that eight 
rows can be covered at a time, with one pipe discharging directly over 
each row. With this outfit from 10 to 12 acres could be covered a 
day using 50 to T5 pounds of dust per acre, at an average cost of from 
$8 to $9.50 per acre, including material and hire of pony and one man. 
Here again it was evident that with some mechanical adjustments, so 
that less dust could be fed into the pipes, and with the speed of the 
fan increased, the amount of dust used per acre could be lowered, and 
the cost reduced accordingly. 



Nicotine Sulphate in a Dust Carrier. 



11 



While the cost per acre with this outfit is hi<2:her than with the hand 
machines, on account of the larger amount of dust used per acre, the 
chief advantage of the power-operated machine is the large acreage 
covered. This would be of importance in sudden or severe outbreaks, 
or on very large plantings. This machine, however, is subject to the 
same objection as the horse-drawn sprayer, only to a less degree, as it 
is smaller, much lighter, and can be drawn bj^ a pony or burro. 

THE PEA APHiy. 

The pea aphis {Macroslphum pisi Kalt.) is present throughout 
California and during some years causes large losses. In fact, in 




Fig. 5. — Iland-oppratert fan duster used against the pea aphis. 

several localities the growing of peas commercially has been largely' 
abandoned because of this pest. This is particularly true of sweet 
peas grown for seed. 

Experiments with the pea aphis have been less extensive than 
with the other insects mentioned, but it has been conclusively proved 
that this pest is much more resistant to the action of nicotine dust 
than any other aphid upon which it has been tested. The low per- 
centages failed absolutely to kill the aphids, but good results were 
obtained with a 10 per cent strength when carefully applied. Sev- 
eral large seed companies have used this strength of dust for two 
seasons, and are much better satisfied with these results than with 
previous control work with liquid sprays. Both hand dusters (fig. 5) 



12 Circular 13^, U. S. Dept. of Agriculture. 

and large power-operated machines, Avliich cover eight rows at a 
time, are used. The hitter use as high as 100 pounds of dust per acre, 
but can cover the ground very rapidly, averaging 3 or 4 acres 
an hour. 

All of the work mentioned in this paper, except the following on 
the pea aphis, was done with dust varying from a week to several 
months old and which had not been kept in tight containers. As 
will be explained later, dust which has stood for some time after 
manufacture loses materially in toxicity, particularly if the containers 
are not tight. It was therefore decided to test on the pea aphis some 
freshly made material Avhich had been immediately put in tight 
cans, applied with a bellows duster to a rather badly infested field 
of peas about a foot high. The results are given in Table ^^ : 

Table 3. — Com txt rat ire cffectireitcss of different streiif/ths of freshly made nico- 
tine HUlphdte dust on the pea apliix at La Hahra, Calif.. Oct. 2<S, 1920. 

Strength of nicotine sulpliate 40 per cent by weiglit (pei- 

cent) 2 3 4 6 

Percentage of aphid.s killed 60.2 70.2 90.9 98.2 

The foregoing experiment showed that the '2 and 3 per cent 
strengths were effective against the young aphids, but quite in- 
effective against the adults, unless the latter were literally coated 
with dust. The application was very liberal, so that, with the 
present - cost of the 6 per cent dust at 20 cents a pound, it would be 
impractical to use it except on sweet peas. Later experiments may 
determine that a smaller amount of dust, or a slightly lower strength, 
will be satisfactory ; but it seems at present that this is the one aphid 
which requires too great a strength of nicotine sulphate to make 
dusting as practical a remedy as spraying. 

ni^Ol^MBEK BEETLES. 

Two pests of considerable importance are the western 12-spotted 
cucumber beetle {Diahi^otlca soror Lee.) and the western strii>ed cu- 
cumber beetle {D. trivitatta Mannh.). The former injures a large 
number of plants, while the latter feeds cliiefly on squash, cucumber, 
and other cucurbits. Wliile Avorking with nicotine sulphate dust on 
the melon aphis, it was observed that the dust was very toxic to the 
occasional specimens of Diabrotica feeding on the melons, and plans 
were made for further experiments against them. A field of young 
cucumber was later examined and found to be badly damaged by 
cucumber beetles. Both D. soror and D. trivitatta were present, but 
the latter was more numerous. Some hills showed little damage, but 
in the majority the foliage was badly eaten and sometimes all the 

=> (3ctol)er, 1920. 



Nicotine Sulphate in a Dust Carrier. 13 

plants in a hill were killed outright. From two to upward of a dozen 
beetles were found in practically every hill. Applications of dust 
were made, using the hand-operated bellows duster. The feed was 
fairly liberal, so that one puff of dust would be sufficient to cover a 
hill. The effect was immediate. When struck with the dust many 
of the beetles were unable to fly away, but crawled about on the 
ground under the plants in very apparent distress, and in a few 
minutes succumbed. Some which were able to fly away, on being 
followed, were found to go only a short distance, and in a very short 
time were overcome. Several days later the field was examined 
again and a careful examination revealed only two living adults in 
the entire field. New leaves had been put out by the injured plants 
and their recovery from attack was apparent. 

The material used was a 10 per cent strength of nicotine sulphate, 
40 per cent in kaolin and lime. A 20 per cent strength was found not 
to be superior to the weaker material. One pound of dust covered 
from 200 to 300 hills of small plants, at the rate of nearly 1,000 hills 
per hour. 

COMBINATIONS WITH NICOTINE SULPHATE DUST. 

It has long been the custom in spraying operations to combine tAvo 
or more insecticides, or an insecticide and a fungicide, when dif- 
ferent types of insects or a disease and an insect are infesting the 
one plant. This practice can be continued to a large extent with 
dusting. In fact, some combinations are more satisfactory in the 
dust form, while others are less so. 

In several sections of California the codling moth has become a 
serious pest of walnuts. It happens that in these same localities, 
to a large extent, the walnut aphis is present also. Therefore when 
the nicotine sulphate dust was made, to each 100 pounds was added 
10 pounds of arsenate of lead. At first the acid form was used, 
but as this caused burning of the foliage the basic or neutral form 
of lead arsenate was substituted. 

At first the dusting was not as satisfactory in controlling the 
codling moth as was desirable. The operation of dusting for the 
aphis could be done quickly and easily, but for the codling moth 
the dust had to be more carefully applied. Although the actual 
percentage of worms killed was a little less with dusting than with 
spraying, dusting is greatly preferred because of the much greater 
speed and ease of application, as well as the lesser cost. 

On cucumbers the nicotine sulphate dust not only controlled the 
cucumber beetles but also killed any melon aphids present. Further- 
more, with the use of a dust carrier containing from 25 to 40 per 
cent of powdered sulphur, the development of cucumber mildew can 
be prevented. 



14 Circular 15^, U. S. Dept. of Agriculture. 

The use of the nicotine sulphate-sulphur dust on peas will control 
both the pea aphis and powdery mildew, and would be equally satis- 
factory for the rose aphis and rose mildew. 

The same combination has proved successful on citrus trees against 
the citrus aphis and the red spider. If anj'' thrips are present, they 
AA'ill be controlled by the same dusting. 

On cabbage the nicotine sulphate dust has given good success in 
killing both the aphis and the cabbage worms, but if it is desired, 
the combination of nicotine sulphate and arsenate of lead can be used. 

Such insects as aphids, thrips, and red spidei^ and other mites re- 
produce very rapidly. Therefore no matter what method of control 
is used, whether it be dusting or spraying, under conditions favorable 
to the insects, a reinfestation may take place even though a high per- 
centage may have been killed. On account of this it is not to be ex-- 
pected that at all times one dusting will be sufficient for an entire 
season. It is often necessary to dust twice or even three times. In 
fact, many growers plan on a second application, timing it to get the 
second infestation before it begins to be serious. 

All dusting and spraying should be done with the idea of pre- 
venting a serious infestation and the resulting damage, rather than 
waiting until the infestation is heavy before control measures are 
undertaken. It is always easier and more satisfactory to prevent an 
infestation than to stop it after it is well under way. 

LOSS OF STRENGTH. 

Since the nicotine in this dust is very volatile, some of the strength 
is apt to be lost if the dust is held for very long in open containers. 
The walnut aphis dust is put up in burlap sacks with paper liners; 
but as this dust is practically all used within a short time after it is 
made, there is little or no loss of strength. To retain the strength, 
it is now proposed to put up the dust in air-tight drums, cans, and 
sealed cartons. It is believed and partly borne out by experiments 
that if these tight containers are used a 8 or 4 per cent strength will 
do as efficient work as has been done heretofore with the 5 to 7i 
per cent strengths put up in sacks, and a 5 or 6 per cent material 
can be substituted for the 8 to 10 per cent strengths. This will 
reduce the cost from 3 to 5 cents a pound. 

Nicotine sulphate dust, even up to the 20 per cent strength, has 
not been observed to cause any burning to foliage. 

For walnut trees the lightest dust possible was found to be desir- 
able; hence the carrier is mostly kaolin. For low-growing crops, 
such as cabbage and melons, a heavier dust is more desirable ; hence 
the carrier was composed of about half kaolin and half lime from 
sujrar-beet factories. 



Nicotine Sulphate in a Dust Carrier. 15 

ADVANTAGES OF DUST. 

Dust can be applied much more easily and quickly than spray; 
hence larger acreages can be covered in a given time. 

Its killing efficiency is always equal to and usually more than that 
of spraying. 

It is easier of application. 

Its cost of application is less than that of spraying. 

Power dusters cost much less than power sprayers. 

Hand dusters are much easier to operate and to carry than hand 
sprayers. 

Very much less weight of dust than of spray is required to cover 
an acre. 

Refilling the duster is much quicker and easier than refilling the 
sprayer. 

It can be combined Avith arsenate of lead or sulphur and applied 
dry for insects and certain fungous diseases. 

DISADVANTAGES OF DUST. 

Its volatility causes it to lose strength unless put up in tight cans 
or used soon after manufacture. 

The dust is sometimes disagreeable to the operator, especially if 
the latter is inexperienced. 

It can not be combined with Bordeaux mixture, except Avlien the 
latter is dry. 

SUMMARY. 

Ground tobacco gave good though varied results in controlling the 
walnut aphis in California. The substitution of a certain amount of 
40 per cent nicotine sulphate in a carrier of kaolin and lime elimi- 
nated this variation in results. 

Dusting requires much less material and may be done in a much 
shorter time, with a less expensive machine, and at about half the 
cost of spraying. 

The action of the dust is similar to that of nicotine sulphate spray, 
but much more rapid. 

Xicotine sulphate dust has proved superior to spraying for the 
melon and cabbage aphids, onion thrips, cucumber beetles, and some 
other insects, giving usually a better killing at a smaller cost and 
with a greater speed and ease of application. 

Nicotine sulphate dust can be combined with arsenate of lead or 
sulphur for different types of insects, or for insects and fungous 
diseases. 

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